Conventional paper and paperboard products are made from hygrocellulosic fibers. These fibers tend to absorb moisture and swell in environments of high humidity and they tend to shrink in low humidity conditions. This dimensional instability in paper and paperboard products leads to problems such as curl, misregistering in printing, bulge, cockle, warp and compressive creep.
For example, a two sided polyethylene extruded release liner was found to exhibit wavy edges in cyclical humidity conditions. This in turn leads to product performance problems such as misregistration in a multicolor printing process.
These end use problems often result in costly project rejects. Thus, there is a need for dimensionally stable paper and paperboard products.
U.S. Pat. No. 3,753,069 to Crawford, U.S. Pat. No. 4,110,155 to Minogawa, U.S. Pat. No. 4,288,287 to Miyama, U.S. Pat. No. 4,331,508 to Miyoma, U.S. Pat. No. 5,178,936 to Kamiya, U.S. Pat. No. 5,194,362 to Nakabayashi, U.S. Pat. No. 5,254,450 to Lacy and U.S. Pat. No. 5,362,614 to Serizawa generally disclose resin coated photographic papers wherein resin stabilizers and/or antioxidants are incorporated into the paper core to help eliminate curl.
The prior art has shown use of sizing agents and paper saturants in the paper industry. Representative of these patents include U.S Pat. Nos. 2,692,183, 2,629,648, 2,629,674 and 2,629,701 to Ericks; U.S. Pat. No. 4,133,688 to Sack, U.S. Pat. No. 4,152,190 to Serota, U.S. Pat. No. 4,522,686 to Dumas, U.S. Pat. No. 4,810,301 to Yoshioka, U.S. Pat. No. 4,849,131 to Sweeney, U.S. Pat. No. 4,935,097 to Tashiro, U.S. Pat. No. 5,160,484 to Nikoloff, and U.S. Pat. No. 5,374,335 to Lindgren.
Unlike the prior art, the present invention overcomes the problems typically associated with hygroreactive cellulosic fibers by providing paper and paperboard products that are more dimensionally stable under cyclical humidity conditions than conventional paper products.
Accordingly, it is a broad object of the invention to provide a dimensionally stable reprographic paper produced by sizing a cellulosic fiber matrix with a hydrophobic material. This technique reduces the hygroexpansion of the paper thus creating more dimensionally stable paper and paperboard products.
Another object of the invention is to reduce hygroexpansion of paper by approximately 40%, therefore creating more dimensionally stable paper and paper board. The technique involves a hydrophobic treatment of the paper which is then dried using heat and/or pressure.
A specific object of the invention is to provide a dimensionally stable release liner that is more stable against moisture changes and lays flat when subjected to cyclical humidity conditions. The base sheet of the release liner is surface sized with a hydrophobic material which permits adhesion of a polyethylene coating without the use of a primer or adhesion coating.
Another more specific object of the invention is to provide a dimensionally stable release liner having a balanced coating, i.e. using the same polyethylene on either side of the base sheet as well as the same coat weight on either side.
Another object of the invention is to provide a dimensionally stable paper or paperboard product with improved lay flat characteristics by surface sizing the base sheet to create a non-hygro reactive paper or paperboard.